Department of Chemistry, Queen's University, Kingston, ON, Canada K7L 3N6.
Org Biomol Chem. 2013 Sep 28;11(36):6047-55. doi: 10.1039/c3ob41204k.
The switchable polarity solvent (SPS) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and an alcohol (e.g. 1-propanol) reversibly switches to a higher polarity ionic liquid, [DBUH(+)][RCO3(-)], when treated with CO2. A long-lived species with unique properties was detected in an investigation into the use of SPS to control the lifetime of the merocyanine (MC) form in a spiropyran (SP)-MC molecular photoswitch. Irradiation of SP in 1-propanol (PrOH) in the presence of DBU generates a new species (λmax = 420 nm). This species converts to MC upon bubbling with CO2, which produces [DBUH(+)][PrOCOO(-)]. It is proposed that a mixture of 1,2 and 1,4 alkoxide addition products form as a result of nucleophilic attack on the conjugated diene system of MC, where alkoxide formation arises from equilibration of highly basic DBU and the alcohol. These adducts revert to MC upon application of CO2 or addition of acid. Determination of the overall equilibrium constant for alkoxide adduct formation involving DBU was afforded through Benesi-Hildebrand analysis.
1,8-二氮杂双环[5.4.0]十一-7-烯（DBU）和醇（例如 1-丙醇）的可切换极性溶剂（SPS）在与 CO2 接触时可逆地切换到更高极性的离子液体[DBUH(+)] [RCO3(-)]。在使用 SPS 控制螺吡喃（SP）-MC 分子光开关中 MC 形式的寿命的研究中，检测到具有独特性质的长寿命物种。在 DBU 存在下，在 1-丙醇（PrOH）中辐照 SP 会生成一种新物种（λmax = 420nm）。该物种在鼓入 CO2 时转化为 MC，生成[DBUH(+)] [PrOCOO(-)]。据推测，由于 MC 的共轭二烯体系受到亲核攻击，形成了 1,2 和 1,4 烷氧基加成产物的混合物，其中烷氧基的形成源于强碱 DBU 和醇之间的平衡。这些加合物在施加 CO2 或添加酸时会恢复为 MC。通过 Benesi-Hildebrand 分析确定了涉及 DBU 的烷氧基加合物形成的总平衡常数。
